Mark the area of crank where it hits and cut it out with electric grinder. Just contour it with at least .050 between the throw and piston. Then get the crank balanced. Doesn't sound like your building alot of power so if the crank needs mallory skip it and just have crank externally balanced. Don't laugh because i buy 8.7 deck cranks from cup engines and grind them for my 8.2 blocksI got a 5.315 rpm i beam and one of your pistons, crashes an rpm internal crank.